Spell checker should be included in reformatting

[tucek]

The spell checker broke my CI build, because i spelled Unix as unix. To prevent unnecessary waiting for the CI to fail on such a trivial issue, i propose to include instructions on how to run the spell checker locally in doc/tutorials/run_reformatting_script_with_docker.md

[markus2330]

Yes, I agree, this is a good idea!

@robaerd can you maybe take a look at it?

[robaerd]

I will include this in #3739.